This invention relates to a method and system for detecting, characterizing and monitoring eye diseases and, particularly, optic nerve diseases, by determining the relative difference in brightness sensed by the two eyes.
Patients who have developed some sort of eye disease typically suffer a loss of visual acuity, an impairment of their visual field, a disparity in color vision, irregular pupillary responses to light, or a combination of two or more of these symptoms. Traditional methods of detecting eye diseases, therefore, have been concerned with measuring the person's visual acuity, visual field, color vision and pupillary responses to light. Additionally, recording of visual evoked responses and measurement of contrast sensitivity have been used to evaluate eye functions and to detect the presence of disease. Of all the above methods, measurement of visual acuity generally has been the most widespread method adopted and used in the neuro-ophthalmic evaluation of eye diseases.
Experience has shown in many instances, however, that measurement of visual acuity is insufficient to detect optic nerve disease. For example, post mortem studies have shown extensive dropout of optic nerve axons in some patients whose visual acuity and general eye examinations have been entirely normal. In one post mortem study of a patient reportedly having no clinical evidence of impaired eye functions, it was estimated that one half of the patient's optic nerve axons had been lost from glaucoma. Additionally, patients who have been diagnosed as having optic neuritis, a form of optic nerve disease, may recover their normal vision, yet still exhibit dysfunction as detected by further clinicial and laboratory tests. Thus, it is apparent that the most widespread method of detecting eye disease is imperfect and inadequate to determine the existence of optic nerve disease.
Measurement of visual acuity also may fail to distinguish among several possible ophthalmological diseases. For example, a patient may have a cataract causing poor vision. If the patient also has optic nerve disease, an operation to remove the cataract would be a useless procedure and pose an unnecessary risk. Unfortunately, the cataract which is causing the poor vision also prevents the ophthalmologist from examining the back of the eyes to attempt to detect the existence of optic nerve disease. Another type of problem may involve a patient with inflamation at the back of the eye, which could be caused by a disease of the retina or of the optic nerve. Even if the ophthalmologist is able to determine that optic nerve disease is present, there are several types of optic nerve disease. Visual acuity tests thus far have been inadequate in distinguishing between the types of optic nerve disease and, further, in monitoring the progression or resolution of the disease once it has been identified.
In 1980, Manister and Dieckert disclosed that color brightness comparison of the eyes may be a useful technique for detecting monocular or asymmetric deficits in optic nerve or macular function. Their method involved presenting a brightly colored test objects to a patient's two eyes and determining whether the eyes perceived the object to be of equal brightness, as described in their article in American Journal of Ophthalmology, Vol. 89, No., 1, pages 58-61 (1980). To determine color brightness differences, they used two polarized trial lenses in a standard trial frame positioned in front of the patient's eyes. The Mainster and Dieckert method, however, focuses on color brightness differences involving red, blue and yellow targets illuminated in a stereoscopic viewer, where an inter-eye disparity in hue perception admittedly renders the method of limited value. Moreover, even if an optic nerve disorder is indicated by a color brightness disparity between the two eyes through their method, there is no disclosure in their article as to how to relate these findings to the nature or extent of the disease. They did not run a clinical study which could suggest how their test results could help in distinguishing among the several types of optic nerve disorders. The device used by Mainster and Dieckert also allows extraneous light to enter laterally between the trial lenses, which obfuscates accurate readings and detracts from the ability to regulate luminance to each eye. In addition, their trial frame system is clumsy and requires frequent recalibration.
Accordingly, there has existed a definite need for a further method of detecting, characterizing and monitoring optic nerve diseases which is not dependent upon the traditional symptoms manifested by a person suffering from eye disease, such as loss of visual acuity, reduction of visual field, disparity in color vision and irregularity of pupillary responses to light. The present invention satisfies this need and provides further related advantages.